The present invention relates to scroll compressor for compressing gas.
FIG. 10 shows such a scroll compressor, which was disclosed in Japanese Unexamined Patent Publication No. 5-321850. The compressor includes a fixed scroll 52 formed in a center housing part 51. A drive shaft 56 is rotatably supported by a front housing part 55. The front housing part 55 and the center housing part 51 form a scroll housing for accommodating a movable scroll 53. A compression chamber 54 is defined between the movable scroll 53 and the fixed scroll 52. The movable scroll 53 is supported by a crank mechanism 56a. The crank mechanism 56a converts rotation of the drive shaft 56 into eccentric (orbital) movement of the movable scroll 53 relative to the drive shaft 56. Orbital movement of the movable scroll 53 causes the volume of the compression chamber 54 to change from the maximum to the minimum and then from the minimum to the maximum. As the volume of the compression chamber 54 is decreased, gas in the compression chamber 54 is compressed.
A compression reaction force generated by compressing gas acts on the rear face 55a of the front housing part 55. Guide holes 55b (only one is shown) are formed in the rear face 55a. Support holes 53b are formed in a base plate 53a of the movable scroll 53. A pin 57 is fitted in each support hole 53b. The distal end of each pin 57 is inserted into the corresponding guide hole 55b. Each pin 57, the corresponding hole 53b and the corresponding guide hole 55b form an anti-rotation mechanism. When rotation of the drive shaft 56 is transferred to the movable scroll 53 by the crank mechanism 56a, the anti-rotation mechanisms prevent the movable scroll 53 from rotating, while permitting the movable scroll 53 to orbit at a predetermined radius.
The diameter of the support holes 53b is slightly greater than the diameter of the pins 57 such that each pin 57 rotates in the corresponding support hole 53b. The pins 57 are supported by the movable scroll 53 in a cantilevered manner. Therefore, when receiving a radial force, each pin 57 is slightly inclined in the corresponding hole 53b. When the movable scroll 53 is orbiting, inclination of the pins 57 causes the load to concentrate at the open end of the hole 53b, which excessively wears the open end of the hole 53b. The wearing of the open end of the holes 53b causes the inclination of the pins 57 to increase. As a result, the orbit radius of the movable scroll 53 eventually exceeds the initial value. A greater orbit radius of the scroll 53 degrades the compression efficiency of the compressor. If the pins 57 are supported by the front housing part 55 and the guide holes are formed in the base plate 53a, the compressor will have the same problem.
In order to prevent the pin 57 from inclining, the proximal end of each pin 57 may be fixed within the corresponding support hole 53b, and a bearing may be fitted to the distal end of each pin 57. The outer surface of the bearing rolls on the wall of the guide hole 55b. This structure prevents the pins 57 from inclining relative to the movable scroll 53. Thus, the holes 53b are not unevenly worn. However, when the compressor is started, the movable scroll 53 is slightly inclined. At this time, each bearing unevenly contacts the open end of the corresponding guide hole 55b. This unevenly wears the bearings and the open end of the guide holes 55b, which eventually increases the orbit radius of the movable scroll 53. Accordingly, the compression efficiency of the compressor is lowered.